Stackable trays have been used for growing mushrooms for many years. Many of these trays are made of wood, are relatively heavy and difficult to move. Additionally, some mushroom trays have a relatively complex structure that are costly to manufacture and maintain. One such tray is disclosed in U.S. Pat. No. 3,992,808 entitled "Mushroom Tray" and issuing to Stengel on Nov. 23, 1996, which is herein incorporated by reference. Therein disclosed is a rectangular wooden tray with four wooden legs tied together by a system of cross bracing. Another container for growing mushrooms is disclosed in U.S. Pat. No. 4,001,966 entitled "Growing Tray Structure, As For Mushrooms" issuing to Metzner on Jan. 11, 1977, which is herein incorporated by reference. Therein disclosed is a structure fabricated of steel-wire mesh affixed to a frame of beam and column supports, and lined with plastic. A plurality of bed structures are stacked. Another mushroom tray is disclosed in U.S. Pat. No. 3,842,534 entitled "Mushroom Tray" and issuing to Walters et al on Oct. 22, 1974, which is herein incorporated by reference. Therein disclosed is a corrosion-resistant extruded aluminum tray with improved air circulation with bottom cross members extending to the side panels. Yet another mushroom tray is disclosed in U.S. Pat. No. 5,040,328 entitled "Mushroom Tray" and issuing to Coon on Aug. 20, 1991, which is herein incorporated by reference. Therein disclosed is a rectangular mushroom tray having corrosion-resistant eye beams positioned to strengthen and stiffen the bottom sheet, and a plurality of clips for securing the eye beams to the underside of the bottom sheet. The trays are made of a polyolefin and the eye beams are made of aluminum. While many of these trays are adequate, they are not suitable for all conditions. For example, while many wooden trays are inexpensive to manufacture, they have a relatively short life and often decompose in the relatively harsh mushroom growing environment, and therefore, generally do not last long. Other tray constructions are relatively complex involving multiple different materials and assemblies, with a considerable amount of structure directed to improving rigidity so that the trays can be stacked and moved with a forklift. The lack of rigidity and complexity of the various structures of the different mushroom trays is a considerable disadvantage, resulting in increasing costs and complexity in the growing and harvesting of mushrooms. These problems are increased, considering the desire to produce larger trays for improved economies of handling. Many of these trays have resulted in failure due to repeated handling and fatigue. Additionally, some of these trays have an undesirable amount of flex resulting in difficult handling and breakage. Therefore, there is a need for an improved, easily manufactured mushroom tray having increased rigidity and longevity.